• Karin Bruun-Plesner, Morten Rune Blichfeldt-Eckhardt, Henrik Bjarke Vaegter, Joergen T Lauridsen, Kirstine Amris, and Palle Toft.
• Pain Research Group, Pain Centre, Odense University Hospital, Odense, Denmark.
• Pain Med. 2020 Oct 1; 21 (10): 2253-2261.

ObjectiveThis study explores dose-response relationships when treating fibromyalgia with low-dose naltrexone.DesignA single-blinded clinical trial was carried out using the "up-and-down" method.SubjectsSubjects included women with a diagnosis of fibromyalgia aged 18-60 years who had been referred to treatment at a public pain clinic at a Danish university hospital.MethodsThe test doses were in the range 0.75-6 mg, and the dosing interval was 0.75 mg. The method was sequential and allowed predicting the dose effective in 50% (ED50) and 95% (ED95) of the subjects when the dose had shifted direction 10 times, and six pairs of "up-and-down" data were available.ResultsA total of 27 subjects were included in the study; two subjects were withdrawn. After inclusion of 25 evaluable subjects, the dose estimates were calculated as 3.88 mg for ED50 and 5.40 mg for ED95. As a secondary outcome, the effects on 10 common fibromyalgia symptoms were evaluated. A high interindividual variation was observed both in the symptom presentation at baseline and in which symptoms were reduced by low-dose naltrexone.ConclusionsThis study is the first to explore dose-response relationships in the treatment of fibromyalgia with low-dose naltrexone. Future placebo-controlled randomized clinical trials are needed, and according to our findings, 4.5 mg, which has previously been used, seems to be a relevant test dose. We recommend that future studies include additional nonpain fibromyalgia symptoms as outcome measures.© The Author(s) 2020. Published by Oxford University Press on behalf of the American Academy of Pain Medicine.All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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